A power take off (PTO) device may be coupled to vehicles for providing power to run accessories such as cement mixers, trash compactors, harvesters, snow ploughs, etc. The PTO may be coupled to the vehicle engine via a drive shaft and may directly derive operational power from engine torque output. During PTO device operation, the engine may be operated at a requested (higher) speed in order to provide a desired torque based on the PTO load.
Various approaches for operating a PTO device have been developed. One example approach shown by Yu et al. in U.S. Pat. No. 7,377,103 discloses a method for PTO device operation wherein power delivery to a PTO device from an engine is initiated upon confirmation that the torque output of the engine is higher than the torque demand of the PTO device. Once a PTO mode is activated by an operator, the engine controller may adjust air and fuel to the engine to maintain the engine speed at an engine speed level required for PTO operation. As such, the PTO device is operated while the vehicle is stationary such that the engine output is adjusted based on the varying PTO load.
However, the inventors herein have recognized potential issues with such systems. As one example, the approach of Yu may not be used while the vehicle is mobile. In particular, an operator may need to propel the vehicle while operating the PTO device. As a result, the engine torque output may need to be adjusted not only for the variation in PTO load but also for the variation in wheel torque during acceleration as well as during deceleration events. If sufficient torque is not provided during tip-in events, the vehicle may appear sluggish and/or the performance of the PTO may degrade. On the other hand, during vehicle deceleration (tip-out of the accelerator pedal), the operator may not be able to optimize pedal position and the engine controller may decrease the engine speed (in view of the decreased driver demand) below the speed desired to sustain the PTO load. As a result, the engine may stall. Therefore, while operating a PTO device, vehicle propulsion including transitions between vehicle accelerating modes and decelerating modes may not be seamless.
In one example, the issues described above may be addressed by a method for a vehicle with a power take off (PTO) device coupled to an engine, comprising: estimating a PTO load based on a difference between engine torque output and torque converter torque output; and adjusting engine torque output based on the estimated PTO load during a transition between engine states. In this way, during vehicle acceleration, a demand for PTO torque may be estimated and used as input for engine speed and torque control during vehicle deceleration events.
As one example, a vehicle may include an engine and a PTO device coupled to the engine. The engine may be coupled to vehicle wheels via a torque converter and a transmission system. A vehicle control system may adjust an engine speed profile based on PTO torque demands as well as vehicle propulsion demands. A vehicle operator may actuate a switch to select between a static PTO mode of operation, wherein a PTO device is operated while the vehicle is stationary, and a mobile PTO mode of operation, wherein the PTO device is operated with the vehicle in motion (vehicle propelled using engine torque). When in the static PTO mode, the controller may adjust each of a throttle position, a spark timing, and a fueling schedule of the engine to adjust the engine speed and engine torque output based on a varying load of the PTO device. If the operator tips in while in the stationary mode, the stationary mode may be exited and the PTO load may not be supported by the engine. Instead, the engine output may be used to propel the vehicle. In the mobile PTO operation mode, during vehicle acceleration events, a raw unfiltered PTO torque demand may be estimated based on engine torque output relative to torque converter torque output. Fluctuations in the PTO torque demand may be estimated and a filtered PTO torque demand may be computed using a variable time constant. The filtered PTO torque demand may be used by the controller in conjunction with the driver torque demand to adjust each of the throttle position, the spark timing, and the engine fueling schedule to run the PTO device while also propelling the vehicle. During a subsequent vehicle deceleration event, the PTO torque learned during the preceding acceleration event may be utilized as input to a target engine speed (Ne) controller (e.g., using proportional-integral-derivative (PID) control) that adjusts the engine torque output (commanded torque) such that torque desired by the PTO device continues to be delivered even as the driver demand reduces.
In this way, by learning a PTO torque demand during vehicle acceleration (as such, PTO may be also estimated during constant speed operation, and deceleration), sufficient torque may continue to be delivered to a PTO device during a subsequent deceleration event. For example, engine speed may be reduced at a slower rate than required based on the drop in driver demand. In addition, the PTO device may be optimally operated even as driver demand changes as well as PTO load changes. The technical effect of controlling engine speed during a tip-out event is that torque desired by the PTO device may be delivered by restricting a decrease in engine speed, thereby pre-empting engine stalls. In addition, PTO devices may be operated under all vehicle driving conditions including both stationary and mobile conditions with reduced possibility of engine stalls and stumbles.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.